My Napa store doesn't mix paint anymore either. They order it from the distribution center. I don't know if all the warehouses have the equipment to do aerosol cans but they can just pick up the phone and get it from another Napa distributor. You gotta go back and talk to the guy at Napa. All you need is the factory color code. They don't need a chip or sample part.
I looked up 69 Vette Daytona yellow and it had two factry codes. I think code 76 is the number you want but it's also code 984.
The Napa part number for this color in acrylic enamel is 30Y-3916. They use different factory codes for Daytona yellow on different years but the 30Y-3916 stayed the same.